Recently there has been interest in motion data capture for use in such fields as graphical animation for movie production and virtual reality. Such motion data is also of interest to sports trainers and athletes to analyze athletic performance. There is also interest by the medical community, for example, in gait analysis. There are two main technologies presently being used to capture the motion data: (1) optical tracking; and (2) electromagnetic tracking.
Optical tracking can provide a high sample rate which is required to capture rapid movement with high resolution. One disadvantage of optical tracking is the potential for obscuring the light sources to the degree that no position solution can be determined. Optical tracking is primarily accomplished using triangulation and multiple light sources, which often requires time-consuming calculations to resolve multiple or visually obscured light sources and detectors. Therefore, the raw motion data is often recorded real-time but analyzed and positions computed off-line at a later time.
Electromagnetic tracking technology does not suffer from the problem of obscured sensors in a metal-free environment. Determination of position and orientation from the electromagnetic sensors can typically be performed in near real-time, however, with just enough delay (typically 4-50 ms) to provide unacceptable disparity between the physical and measured motion. The delay is largely due to the physics of the technology which requires the electromagnetic signal be transmitted, received, filtered and analyzed. Current devices provide a maximum sample rate of only about 120 Hz, while a sampling rate of from about 200 to 300 Hz is required to have an acceptable data resolution for rapid movement. The delay has made the electromagnetic devices unacceptable in applications requiring the tracking of rapid movements in real-time, e.g., conversion of human motion to music, while the slow sampling rate means the electromagnetic devices provide data with unacceptable resolution for tracking rapid athletic motion, such as a golf, tennis or batting swing.
There is, therefore, a need for a system which does not suffer from the shortcomings of the present optical and electromagnetic tracking systems, while providing a high rate of orientation and position data in real-time.